A commonly used floor/ceiling system uses wood decks placed over wood joists. These systems may include insulation and layers of gypsum drywall attached to the joist using acoustical channels. To provide improved acoustical performance, these decks are frequently covered with a mat with acoustical properties such as USG LEVELROCK Brand SRB (sound reduction board) or USG LEVELROCK Brand SRM-25 (sound reduction mat), and a poured gypsum underlayment such as USG LEVELROCK Brand underlayment. One limitation of these wood systems is that they cannot be used in structures requiring “non-combustible design,” such as some multi-story residential and commercial buildings, schools and hospitals.
To provide a “non-combustible design,” a common floor/ceiling system includes construction using steel deck systems over steel framing. These typically involve a design using a system of corrugated steel decking, designed using steel properties provided by the Steel Deck Institute (SDI) applied over steel joists and girders. The steel deck is then covered with concrete. The concrete is typically 2-4 inches thick and reinforced with reinforcing steel. The concrete provides additional strength to the floor to permit it to carry design loads and limit floor deflections. A ceiling, such as gypsum drywall mounted on DIETRICH RC DELUXE channels may be attached to the bottoms of the joists or ceiling tiles and grid may be hung from the joists. An alternate is for the bottom surfaces of the steel to be covered with spray fiber or fireproofing materials. Limitations of these systems include increased construction times due to placement and curing of the lightweight concrete, lower acoustical performance, and overall weight of the system.
In existing systems, the concrete is used with the steel deck and joists to provide the flexural and diaphragm strengths required for the structure. The designs cannot accommodate the full design load capacity until after the concrete has fully cured, which is normally a period of up to 28 days. Load restrictions may be in place until after 28 days. The concrete also is required to be cured, which may involve the placement of wetted burlap on the floor or the addition of a curing compound on the floor. Additional details of curing are documented by the American Concrete Institute Committee 308 “Standard Practice for Curing Concrete” (ACI 308, American Concrete Institute, Farmington Hills, Mich.) If used, curing blankets and films, often left for up to 7 to 14 days after concrete placement, prohibit trades persons from getting back on the job for work, such as installation of gypsum wallboard.
Floor sound ratings are typically evaluated in a laboratory by ASTM Standards E492 or and E989 and are rated as to impact insulation class (IIC). The greater the IIC rating, the less impact noise will be transmitted to the area below. In general, impact sound is generated due to pedestrian footfall on the floor, movement of heavy objects over the floor and any other contact made with the floor.
Floors may also be rated as to Sound Transmission Class (STC) using ASTM E90. The greater the STC rating, the less airborne sound will be transmitted to the area below. Airborne sound is usually due to speech or music.
The acoustic performance with respect to Impact Insulation Class (IIC) of typical metal deck systems with a ceiling including 4 inches of concrete over steel decking is generally poor, rating frequently less than 35. Without a ceiling these systems would provide IIC ratings frequently less than 25. A poor rating particularly results if the flooring is covered with hard surfacing, such as ceramic tile, wood or vinyl.
The use of carpeting is one approach taken to addressing the problem of the transmission of impact sound between floors in multistory dwellings and commercial buildings. However, this is not always practical. An alternative to the use of carpeting to prevent impact sound transmission has been the use of a floating floor or other sound rated floor system. Ceilings may also be adjusted to improve the impact sound performance of a floor. These may be attached using various clips or channels including RC1, PAC-international RSIC, DWSS or various other systems to provide sound isolation.
Sound rated floors typically are required by building codes to have an IIC rating of not less than 50 and an STC rating of not less than 50. Even though an IIC rating of 50 meets many building codes, experience has shown that in luxury condominium applications, even floor-ceiling systems having an IIC of 56-57 may not be acceptable because some impact noise is still audible. Every 10 points of increase in IIC rating represents a doubling of performance and would sound half as audible to the human ear.
Also, a sound rated floor must have enough strength and stiffness to limit the potential for cracking and deflection of the finished covering. At the same time, the sound rated floor should be resilient enough to isolate the impact noise from the area to be protected below.
Also, a sound rated floor with a relatively low profile is preferred to maintain minimum transition heights between a finished surface of the sound rated floor and adjacent areas, such as carpeted floors, which by themselves may have sufficiently high IIC ratings.
U.S. Pat. No. 4,685,259 discloses a sound rated flooring which comprises a sound attenuation layer placed on a subfloor. The panel structure has a core and at least one acoustically semi-transparent facing of fibrous material bonded to the core and a rigid layer on the sound attenuation layer. The core of the panel structure is a walled structure such as a honeycomb formed of cardboard, kraft paper or aluminum. The facing placed on the core is a fibrous material such as glassfiber. A rigid layer is placed on top of the attenuation layer to support the upper finished flooring.
In a floating floor system, an intervening sound isolating layer is incorporated between the top finish surface and the floor joists. U.S. Pat. No. 4,879,856 discloses a floating floor system for use with joist floors. Inverted channel section floor supports are mounted longitudinally on the floor joists. The inverted channel has outwardly directed flanges between the joists. Sound insulation material is interposed on the outward directed flanges between the joists. The flooring is extended over the insulation material and secured to the joists.
U.S. Pat. No. 4,681,786 discloses a horizontal-disassociation-cushioning layer underneath a tile floor. The horizontal-disassociation-cushioning layer is a sheet of elastic foam from about ⅛ to ½ inch thick used to diminish the transmission of impact sound to the area below the floor.
Isolation media for use in sound rated floors also include USG LEVELROCK brand sound reduction board, USG LEVELROCK brand sound reduction mats, and MAXXON ACOUSTI-MAT II or ACOUSTI-MAT III brand sound reduction mats. In a typical use, the mat or board is laid over an entire concrete or wood subfloor. Then isolation strips are installed, and then taped around the perimeter of the entire room, to eliminate flanking paths. Then seams between sections of the sound reduction mat or board are adhered with zip-strips or taped. Then the sound reduction mat or board is covered with ¾ to one -inch (18 to 25 mm) of an underlayment such as LEVELROCK brand floor underlayment. To ensure uniform depth and a smooth finish, installers may use a “screed” to finish the underlayment surface.